One of the most high-profile defectors to flee North Korea says he left due to growing disillusionment with life under the country's leader, Kim Jong-un.
Thae Yong-ho, a former deputy envoy to London, defected to the South in August.
Speaking to a South Korean parliamentary committee, he said North Koreans were living in conditions amounting to slavery.
After his defection North Korea called him "human scum".
The North's state media said the envoy had been accused of leaking secrets, embezzlement and child rape.
South Korea announced in August that Mr Thae had arrived with his family. Since then he has been undergoing intensive interrogation from the intelligence services aimed at weeding out spies.
According to politician Lee Cheol-Woo, who met Mr Thae, he had become increasingly aware of the "gruesome realities" of life in North Korea.
"There are many ranking North Korean officials suffering from depression over concerns they will have to live like slaves for a long time if the North's young leader rules the country for decades," Mr Lee quoted him as saying.
Mr Thae is also reported to have said he learned about South Korean democracy through watching South Korean films and dramas.
The Sunday Express has reported that Mr Thae was allegedly ordered by his superiors to try to bribe a UK Ministry of Defence civil servant or naval officer into revealing nuclear secrets - a big factor, the newspaper says, in his decision to defect.
About 1,000 people defect from North Korea each year, fleeing a repressive state that has faced numerous accusations of human rights abuses.
The South says it has seen a surge in defections from people with privileged backgrounds, suggesting cracks in the North's government, Yonhap reports.